What bacterial pathogens possess pathogenicity islands that contribute to their ability to cause disease?

Bacterial Pathogens with Pathogenicity Islands Contributing to Disease

Many important bacterial pathogens possess pathogenicity islands that significantly enhance their virulence capabilities, including Salmonella, Escherichia coli, Staphylococcus aureus, Yersinia, Shigella, Pseudomonas, Bordetella, and Chlamydia species. 1

What Are Pathogenicity Islands?

Pathogenicity islands (PAIs) are specialized mobile genetic elements that:

• Comprise large genomic regions (10-200 kilobases in size)
• Are present in pathogenic strains but absent in non-pathogenic relatives
• Often have G+C content different from the rest of the bacterial genome
• Frequently contain direct repeats at their ends
• Are often associated with tRNA genes
• Contain integrase determinants and other mobility loci
• Show genetic instability
• Were likely acquired through horizontal gene transfer 2, 3

Key Bacterial Pathogens with Pathogenicity Islands

1. Enterobacteriaceae Family

• Escherichia coli

  • Pathogenic strains (especially enterohemorrhagic E. coli) contain PAIs that encode virulence factors
  • Demonstrates enormous genomic variation with a pangenome of over 16,000 genes 4
  • Different strains can be neutral to the host, enterohemorrhagic, or even probiotic, depending on their genetic content 4

• Salmonella species

  • Possess excisable PAIs that contribute to virulence 5
  • Contain type III secretion systems encoded by PAIs 1
  • Have special predilection for vascular tissue, particularly in patients with atherosclerotic disease 6
  • S. enteritidis and S. choleraesuis specifically target vascular tissue 6

• Klebsiella pneumoniae

  • Increasingly showing antimicrobial resistance through extended-spectrum β-lactamase (ESBL) production 4

2. Non-Fermenters

• Pseudomonas aeruginosa

  • Contains type III secretion systems encoded by PAIs 1
  • Common cause of complicated skin and soft tissue infections (12.1% of isolates) 4
  • Important pathogen in healthcare-associated pneumonia 4

• Acinetobacter baumannii

  • Increasingly showing carbapenem resistance (CRAB) 4
  • Considered a critical threat pathogen by WHO 4

3. Gram-Positive Pathogens

• Staphylococcus aureus

  • Contains a large family of pathogenicity islands (SaPIs) encoding superantigens and other virulence factors 7
  • SaPIs are mobilized by helper phages and transferred at extremely high frequencies 7
  • Shows large intra-species genomic variation with a pangenome approximately five times larger than its core genome 4
  • Methicillin-resistant strains (MRSA) are particularly concerning in community and healthcare settings 4

• Streptococcus pneumoniae

  • Major cause of community-acquired pneumonia 4

4. Other Important Pathogens

• Bordetella pertussis and B. parapertussis

  • Contain type III secretion systems encoded by PAIs 1
  • Causative agents of pertussis (whooping cough) 4

• Chlamydia species

  • Possess type III secretion systems encoded by PAIs 1

• Yersinia species

  • Contain type III secretion systems encoded by PAIs 1

Functional Significance of Pathogenicity Islands

Type III Secretion Systems

Many PAIs encode type III secretion (TTS) systems that:

• Facilitate contact-dependent secretion of virulence factors
• Allow direct delivery of bacterial toxins into host cells
• Play crucial roles in host-pathogen interactions 1

Virulence Mechanisms

PAIs encode various virulence factors including:

• Adhesins (for attachment to host tissues)
• Toxins (that damage host cells)
• Invasins (facilitating bacterial entry into cells)
• Protein secretion systems
• Iron uptake systems 3

Clinical Implications

Antimicrobial Resistance

• Many pathogens with PAIs also show concerning antimicrobial resistance patterns
• ESBL-producing E. coli and K. pneumoniae can negatively affect patient outcomes 4
• Carbapenem-resistant organisms (CRE, CRAB, CRPA) are listed as critical threats by WHO 4

Disease Manifestations

• Pathogens with PAIs can cause a wide spectrum of diseases:
  • Complicated skin and soft tissue infections
  • Intra-abdominal infections
  • Pneumonia
  • Bloodstream infections
  • Endovascular infections 4, 6

Treatment Challenges

• The presence of PAIs often correlates with more virulent infections
• May require combination antimicrobial therapy
• Surgical intervention is often necessary for complicated infections 4

Future Perspectives

• PAIs represent potential targets for novel therapeutic approaches
• Understanding PAI mobility and transfer mechanisms may help predict the emergence of new pathogens
• PAIs could potentially be used as delivery systems for vaccination or new treatment strategies 2